The objective of the proposed research is to identify and characterize properties of the epithelial surface of the uterus which are involved in trophoblast adhesion and subsequent invasion during implantation. The research will test the hypothesis that the epithelium serves as the primary site for mediation of hormonally-modulated receptiveness of the uterus to blastocyst implantation. Aims of the project include 1) the use of biochemical methods to identify and isolate uterine and trophoblast membrane molecules which bind specifically to one another in complementary receptor/ligand interactions, 2) to validate the structural and biochemical properties of an in vitro uterine epithelial system as a model for the receptive uterine surface, and to refine the system as appropriate, and 3) to use the epithelial cultures to examine trophoblast-uterine adhesion and to test the functional roles of the receptor/ligand molecules identified under Aim 1. The model, as studied to date, offers promise for allowing identification of maternal and embryonic factors required for cell-cell adhesion and fusion between these genetically disparate tissues. Results will be applicable to elucidating problems in cell-interaction generally and, more specifically, to the process of establishing pregnancy.